Controlling the temperature of a substrate in a film deposition apparatus

ABSTRACT

A system and method for that allows one part of an atomic layer deposition (ALD) process sequence to occur at a first temperature while allowing another part of the ALD process sequence to occur at a second temperature. In such a fashion, the first temperature can be chosen to be lower such that decomposition or desorption of the adsorbed first reactant does not occur, and the second temperature can be chosen to be higher such that comparably greater deposition rate and film purity can be achieved. Additionally, the invention relates to improved temperature control in ALD to switch between these two thermal states in rapid succession.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent applicant Ser. No.10/900,830, filed on Jul. 28, 2004, incorporated herein by reference,which is a division of U.S. patent application Ser. No. 09/854,092,filed on May 10, 2001, and incorporated herein by reference, which is acontinuation-in-part of U.S. application Ser. No. 09/812,285, now U.S.Pat. No. 6,428,859, U.S. application Ser. No. 09/812,352, now abandoned,and U.S. application Ser. No. 09/812,486, now U.S. Pat. No. 6,416,822;all filed Mar. 19, 2001. All of these prior applications claim thebenefit of U.S. Provisional Application No. 60/251,795, filed Dec. 6,2000, and U.S. Provisional Application No. 60/254,280, filed Dec. 6,2000.

FIELD OF THE INVENTION

The present invention relates to the field of film deposition, and moreparticularly, to a method and apparatus for improving and enhancingtemperature control in atomic layer deposition (ALD).

BACKGROUND

The present invention relates generally to the field of advanced thinfilm deposition methods commonly used in the semiconductor, datastorage, flat panel display, as well as allied and other industries.More particularly, the present invention relates to improved atomiclayer deposition whereby the kinetics of the adsorption of the firstprecursor and the subsequent reaction with the second precursor aredecoupled. By decoupling, we mean causing the reaction (i.e.,adsorption) of the first precursor to occur at a different temperaturestate than the temperature state required for the reaction with thesecond precursor. More importantly, methods and apparatus for improvedtemperature control in ALD are disclosed that can switch between thesetwo thermal states in rapid succession.

The disadvantages of conventional ALD are additionally discussed incopending applications with the same assignee entitled “SequentialMethod For Depositing A Film By Modulated Ion-Induced Atomic LayerDeposition (MII-ALD)”, “System and Method for Modulated Ion InducedAtomic Layer Deposition (MII-ALD)”, and “Continuous Method ForDepositing A Film By Modulated Ion-Induced Atomic Layer Deposition(MII-ALD)” which are hereby incorporated by reference in their entiretyand may be found as copending utility applications, application Ser.Nos. 09/812,285, 09/812,352, 09/812,486 respectively.

As integrated circuit (IC) dimensions shrink and the aspect ratios ofthe resulting features increase, the ability to deposit conformal,ultra-thin films on the sides and bottoms of high aspect ratio trenchesand vias becomes increasingly important. These conformal, ultra-thinfilms are typically used as “liner” materials to enhance adhesion,prevent inter-diffusion and/or chemical reaction between the underlyingdielectric and the overlying metal, and promote the deposition of asubsequent film.

In addition, decreasing device dimensions and increasing devicedensities has necessitated the transition from traditional CVD tungstenplug and aluminum interconnect technology to copper interconnecttechnology. This transition is driven by both the increasing impact ofthe RC interconnect delay on device speed and by the electromigration(i.e., the self-diffusion of metal along interconnects, therebyaffecting reliability) limitations of aluminum based conductors for sub0.25 μm device generations. Copper is preferred due to its lowerresistivity and higher (more than 10 times) electromigration resistanceas compared to aluminum. A single or dual damascene copper metallizationscheme is used since it eliminates the need for copper etching andreduces the number of integration steps required. However, the burdennow shifts to the metal deposition step(s) as the copper must fillpredefined high aspect ratio trenches and/or vias in the dielectric.Electroplating has emerged as the copper fill technique of choice due toits low deposition temperature, high deposition rate, and potential lowmanufacturing cost.

Two major challenges exist for copper wiring technology: the barrier andseed layers. Copper can diffuse readily into silicon and mostdielectrics. This leads to electrical leakage between metal wires andpoor device performance. An encapsulating barrier layer is needed toisolate the copper from the surrounding material (e.g., dielectric, Si),thus preventing copper diffusion and/or reaction with the underlyingmaterial (e.g., dielectric, Si). In addition, the barrier layer alsoserves as the adhesion or glue layer between the patterned dielectrictrench or via and the copper used to fill it. The dielectric materialcan be a low dielectric constant i.e., low-k material (used to reduceinter- and intra-line capacitance and cross-talk) which typicallysuffers from poorer adhesion characteristics and lower thermal stabilitythan traditional oxide insulators. Consequently, this places morestringent requirements on the barrier material and deposition method. Aninferior adhesion layer will, for example, lead to delamination ateither the barrier-to-dielectric or barrier-to-copper interfaces duringany subsequent anneal and/or chemical mechanical planarization (CMP)processing steps leading to degradation in device performance andreliability. Ideally, the barrier layer should be thin, conformal,defect free, and of low resistivity so as to not compromise theconductance of the copper metal interconnect structure.

In addition, electroplating fill requires a copper seed layer, whichserves to both carry the plating current and act as the nucleationlayer. The preferred seed layer should be smooth, continuous, of highpurity, and have good step coverage with low overhang. A discontinuityin the seed layer will lead to sidewall voiding, while gross overhangwill lead to pinch-off and the formation of top voids.

Both the barrier and seed layers which are critical to successfulimplementation of copper interconnects require a means of depositinghigh purity, conformal, ultra-thin films at low substrate temperatures.

Physical vapor deposition (PVD) or sputtering has been adopted as thepreferred method of choice for depositing conductor films used in ICmanufacturing. This choice has been primarily driven by the low cost,simple sputtering approach whereby relatively pure elemental or compoundmaterials can be deposited at relatively low substrate temperatures. Forexample, refractory based metals and metal compounds such as tantalum(Ta), tantalum nitride (TaN_(x)), other tantalum containing compounds,tungsten (W), tungsten nitride (WN_(x)), and other tungsten containingcompounds which are used as barrier/adhesion layers can be sputterdeposited with the substrate at or near room temperature. However, asdevice geometries have decreased, the step coverage limitations of PVDhave increasingly become an issue since it is inherently a line-of-sightprocess. This limits the total number of atoms or molecules which can bedelivered into the patterned trench or via. As a result, PVD is unableto deposit thin continuous films of adequate thickness to coat the sidesand bottoms of high aspect ratio trenches and vias. Moreover,medium/high-density plasma and ionized PVD sources developed to addressthe more aggressive device structures are still not adequate and are nowof such complexity that cost and reliability have become seriousconcerns.

Chemical vapor deposition (CVD) processes offer improved step coveragesince CVD processes can be tailored to provide conformal films.Conformality ensures the deposited films match the shape of theunderlying substrate, and the film thickness inside the feature isuniform and equivalent to the thickness outside the feature.Unfortunately, CVD requires comparatively high deposition temperatures,suffers from high impurity concentrations which impact film integrity,and have higher cost-of-ownership due to long nucleation times and poorprecursor utilization efficiency. Following the tantalum containingbarrier example, CVD Ta and TaN films require substrate temperaturesranging from 500 degrees C. to over 800 degrees C. and suffer fromimpurity concentrations (typically of carbon and oxygen) ranging fromseveral to tens of atomic % concentration. This generally leads to highfilm resistivities (up to several orders of magnitude higher than PVD),and other degradation in film performance. These deposition,temperatures and impurity concentrations make CVD Ta and TaN unusablefor IC manufacturing, in particular for copper metallization and low-kintegration.

Chen et al. (“Low temperature plasma-assisted chemical vapor depositionof tantalum nitride from tantalum pentabromide for coppermetallization”, J. Vac. Sci. Technol. B 17(1), pp. 182-185 (1999); and“Low temperature plasma-promoted chemical vapor deposition of tantalumfrom tantalum pentabromide for copper metallization”, J. Vac. Sci.Technol. B 16(5), pp. 2887-2890 (1998)) have demonstrated aplasma-assisted (PACVD) or plasma-enhanced (PECVD) CVD approach usingtantalum pentabromide (TaBr₅) as the precursor to reduce the depositiontemperature. Ta and TaN_(x) films were deposited from 350 degrees C. to450 degrees C. and contained 2.5 to 3 atomic % concentration of bromine.Although the deposition temperature has been reduced by increasedfragmentation (and hence increased reactivity) of the precursor gases inthe gas phase via a plasma, the same fragmentation leads to thedeposition of unwanted impurities. Gas-phase fragmentation of theprecursor into both desired and undesired species inherently limits theefficacy of this approach.

Recently, atomic layer chemical vapor deposition (AL-CVD) or atomiclayer deposition (ALD) has been proposed as an alternative method to CVDfor depositing conformal, ultra-thin films at comparatively lowertemperatures. ALD is similar to CVD except that the substrate issequentially exposed to one reactant at a time. Conceptually, it is asimple process: a first reactant is introduced onto a heated substratewhereby it forms a monolayer on the surface of the substrate. Excessreactant is pumped out. Next a second reactant is introduced and reactswith the first reactant to form a monolayer of the desired film via aself-limiting surface reaction. The process is self-limiting since thedeposition reaction halts once the initially adsorbed (physi- orchemisorbed) monolayer of the first reactant has fully reacted with thesecond reactant. Finally, the excess second reactant is evacuated. Theabove sequence of events comprises one deposition cycle. The desiredfilm thickness is obtained by repeating the deposition cycle therequired number of times.

In practice, ALD is complicated by the painstaking selection of aprocess temperature setpoint wherein both: 1) at least one of thereactants sufficiently adsorbs to a monolayer and 2) the surfacedeposition reaction can occur with adequate growth rate and film purity.If the substrate temperature needed for the deposition reaction is toohigh, desorption or decomposition of the first adsorbed reactant occurs,thereby eliminating the layer-by-layer process. If the temperature istoo low, the deposition reaction may be incomplete (i.e., very slow),not occur at all, or lead to poor film quality (e.g., high resistivityand/or high impurity content). Since the ALD process is entirelythermal, selection of available precursors (i.e., reactants) that fitthe temperature window becomes difficult and sometimes unattainable. Dueto the above-mentioned temperature-related problems, ALD has beentypically limited to the deposition of semiconductors and insulators asopposed to metals.

Continuing with the TaN example, ALD of TaN films is confined to anarrow temperature window of 400 degrees C. to 500 degrees C., generallyoccurs with a maximum deposition rate of 0.2 angstroms/cycle, and cancontain up to several atomic percent of impurities including chlorineand oxygen. Chlorine is a corrosive, can attack copper, and lead toreliability concerns. The above process is unsuitable for coppermetallization and low-k integration due to the high depositiontemperature, slow deposition rate, and chlorine impurity incorporation.

In conventional ALD of metal films, gaseous hydrogen (H₂) or elementalzinc (Zn) is often cited as the second reactant. These reactants arechosen since they act as a reducing agent to bring the metal atomcontained in the first reactant to the desired oxidation state in orderto deposit the end film. Gaseous, diatomic hydrogen (H₂) is aninefficient reducing agent due to its chemical stability, and elementalzinc has low volatility (e.g., it is very difficult to deliversufficient amounts of Zn vapor to the substrate) and is generallyincompatible with IC manufacturing. Unfortunately, due to thetemperature conflicts that plague the ALD method and lack of kineticallyfavorable second reactant, serious compromises in process performanceresult.

In order to address the limitations of traditional thermal or pyrolyticALD, radical enhanced atomic layer deposition (REALD, U.S. Pat. No.5,916,365) or plasma-enhanced atomic layer deposition has been proposedwhereby a downstream radio-frequency (RF) glow discharge is used todissociate the second reactant to form more reactive radical specieswhich drives the reaction at lower substrate temperatures. Using such atechnique, Ta ALD films have been deposited at 0.16 to 0.5angstroms/cycle at 25 degrees C., and up to 1.67 angstroms/cycle at 250degrees C. to 450 degrees C. Although REALD results in a lower operatingsubstrate temperature than all the aforementioned techniques, theprocess still suffers from several significant drawbacks. Highertemperatures must still be used to generate appreciable depositionrates. However, such temperatures are still too high for some films ofsignificant interest in IC manufacturing such as polymer-based low-kdielectrics that are stable up to temperatures of only 200 degrees C. orless. REALD remains a thermal or pyrolytic process similar to ALD andeven CVD since the substrate temperature provides the requiredactivation energy for the process and is therefore the primary controlmeans for driving the deposition reaction.

In addition, Ta films deposited using REALD still contain chlorine aswell as oxygen impurities, and are of low density. A low density orporous film leads to a poor barrier against copper diffusion sincecopper atoms and ions have more pathways to traverse the barriermaterial. Moreover, a porous or under-dense film has lower chemicalstability and can react undesirably with overlying or underlying films,or with exposure to gases commonly used in IC manufacturing processes.

Another limitation of REALD is that the radical generation and deliveryis inefficient and undesirable. RF (such as 13.56 MHz) plasma generationof radicals used as the second reactant such as atomic H is not asefficient as microwave plasma due to the enhanced efficiency ofmicrowave energy transfer to electrons used to sustain and dissociatereactants introduced in the plasma. Furthermore, having a downstreamconfiguration whereby the radical generating plasma is contained in aseparate vessel located remotely from the main chamber where thesubstrate is situated and using a small aperture to introduce theradicals from the remote plasma vessel to the main chamber bodysignificantly decreases the efficiency of transport of the secondradical reactant. Both gas-phase and wall recombination will reduce theflux of desired radicals that can reach the substrate. In the case ofatomic H, these recombination pathways will lead to the formation ofdiatomic H₂, a far less effective reducing agent. If the plasma used togenerate the radicals was placed directly over the substrate, then thedeposition of unwanted impurities and particles can occur similarly tothe case of plasma-assisted CVD.

Finally, ALD (or any derivative such as REALD) is fundamentally slowsince it relies on a sequential process whereby each deposition cycle iscomprised of at least two separate reactant flow and evacuation stepswhich can occur on the order of minutes with conventional valve andchamber technology. Significant improvements resulting in faster ALD areneeded to make it more suitable for commercial IC manufacturing.

SUMMARY OF THE INVENTION

A method for depositing a film on a substrate in a chamber comprisingadjusting a temperature of said substrate to a first temperature,introducing a first reactant gas into said chamber, adsorbingsubstantially at least one monolayer of said first reactant gas ontosaid substrate, evacuating any excess of said first reactant gas fromsaid chamber, adjusting a temperature of said substrate to a secondtemperature, introducing a second reactant gas into said chamber toreact with said first reactant gas to produce said film on saidsubstrate, and evacuating any excess of said second reactant gas fromsaid chamber; and adjusting a temperature of said substrate to a thirdtemperature.

A system for depositing a film on a substrate in a chamber comprising ameans for adjusting a temperature of said substrate to a firsttemperature, a means for introducing a first reactant gas into saidchamber, a means for adsorbing substantially at least one monolayer ofsaid first reactant gas onto said substrate, a means for evacuating anyexcess of said first reactant gas from said chamber, a means foradjusting a temperature of said substrate to a second temperature, ameans for introducing a second reactant gas into said chamber to reactwith said first reactant gas to produce said film on said substrate, ameans for evacuating any excess of said second reactant gas from saidchamber, and a means for adjusting a temperature of said substrate to athird temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the relative timing diagram of the sequence for theimproved ALD method incorporating two (or more) discrete temperaturestates;

FIG. 2 shows the relative timing diagram of an alternative sequence forthe improved ALD method incorporating two (or more) discrete temperaturestates;

FIG. 3 is the ALD system schematic incorporating a lamp array forrapidly heating, and a chilled electrostatic chuck (ESC) for rapidlycooling, the substrate;

FIG. 4 is the ALD system schematic incorporating a mechanically-scannedlaser (coupled with wafer rotation) for rapidly heating, and a chilledelectrostatic chuck (ESC) for rapidly cooling, the substrate; and

FIG. 5 shows the relative timing diagram of substrate temperatureresponse to irradiation and state-dependent control of backside gaspressure.

DETAILED DESCRIPTION OF THE INVENTION

The present invention resolves the ALD temperature dilemma revolvingaround the use of a single, fixed substrate temperature setpoint as theprincipal means of controlling or driving the deposition reaction. Thepresent invention does this by allowing one part of the ALD processsequence (e.g., adsorption of the first reactant) to occur at a firsttemperature (typically lower) while allowing another part of the ALDprocess sequence (e.g., reaction between the second reactant with theadsorbed first reactant) to occur at a second temperature (typicallyhigher). In such a fashion, the first temperature can be chosen to be alower level such that decomposition or desorption of the adsorbed firstreactant does not occur, and the second temperature can be chosen to beof a higher level such that comparably greater deposition rate and filmpurity can be achieved. More importantly, the invention relates tomethods and apparatuses for improved temperature control in ALD that canswitch between these two thermal states in rapid succession. Via thesemethods and apparatuses, the limitations in precursor choice can beresolved while improving process performance and deposition rate. Inparticular, precursor choice can be expanded to include metals—a highlydesirable class of materials previously not viable with conventionalALD.

Since ALD is by definition a slow process, introducing a secondtemperature state would typically compete with the desire to increaseprocessing speed, i.e., the ALD flow-evacuate-flow-evacuate sequencewould take even longer. This would be especially true in a conventional,isothermal hot-wall or resistively heated pedestal reactor systemcommonly used for ALD. This is because the reactor or pedestal must beheated to a higher temperature and then cooled to a lower temperature,which can take several minutes, or greater, due to the large thermalmasses involved. Since each deposition cycle results in a film thicknessof at most one monolayer, the process would be extremely slow (muchslower than even conventional ALD and its derivatives) and highlyunfavorable for IC device manufacturing. However, methods exist torapidly impart energy into a substrate (which may be a “bare” substrate,e.g., a silicon wafer before any films have been deposited, or it may bea substrate which may already have had one or more films deposited onits surface), either globally or in a focused or otherwise localizedfashion, causing a transient, rather than quasi-static, change insubstrate temperature. The substantial process benefits of employingsuch methods, in particular improved adsorption and stability of thefirst reactant plus substantially increased deposition rate,significantly outweigh the increased complexity.

FIG. 1 shows a sequence for an improved ALD method incorporating two (ormore) discrete temperature states. In the variant of the method shown inFIG. 1, the substrate temperature is ramped 134 during the evacuation124 of the first reactant. Note that the time axis is not to scale. FIG.2 shows an alternative sequence for an improved ALD method incorporatingtwo (or more) discrete temperature states. In the variant of the methodshown in FIG. 2, the substrate temperature is ramped 234 during the flow212 of the second reactant. Again, note that the time axis is not toscale.

An improved ALD sequence incorporating the aforementioned invention isas follows:

1. First exposure 100, 200: During a gas evacuation 120, 122, 222, asubstrate is heated (or cooled) to a first temperature, T₁ 132, 232, isexposed 102, 202 to a first gaseous reactant, allowing a monolayer ofthe reactant to form on the surface.

2. First evacuation: The excess reactant is removed by evacuating 124,224 the chamber with a vacuum pump. An inert gas purge (e.g., Ar or He)can be used in conjunction to speed evacuation/removal of any excessfirst reactant. In some cases, the purge gas can be diatomic hydrogen(H₂) due to its low reactivity to the first reactant.

3. Second exposure 110, 210: The substrate is then heated (or cooled) toa second temperature, T₂ 134, 136, 234, 236, where T₂ 136, 236 is notequal to T₁ 132, 232. A second gaseous reactant is introduced 112, 212into the reactor chamber and onto the substrate. The first and second(chemi- or physi-sorbed) reactants react to produce a solid thinmonolayer of the desired film. The reaction between the first and secondreactants is self-limiting in that the reaction between them terminatesafter the initial monolayer of the first reactant is consumed.

4. Second evacuation 126, 226: The excess second reactant is removed byagain evacuating 126, 226 the chamber with the vacuum pump. An inert gaspurge (e.g., Ar or He) can be used in conjunction to speedevacuation/removal of any excess first reactant. In some cases, thepurge gas can be diatomic hydrogen (H₂) due to its low reactivity to thefirst reactant. The substrate is then cooled (or heated) back to a firsttemperature, T₁ 138, 139, 238, 239.

5. Repeat: The desired film thickness is built up by repeating theentire process cycle (steps 1-4) many times.

Additional precursor gases may be introduced and evacuated as requiredfor a given process to create tailored films of varying compositions ormaterials.

Preferably, T₂ 136, 236 is greater than T₁ 132, 232. The firsttemperature, T₁ 132, 232, needs to be low enough so that the firstreactant sufficiently forms a monolayer and does not decompose or desorbfrom the substrate. However, T₂ 136, 236 must be high enough in order todrive the deposition reaction and improve film purity. Typically, T₁132, 232 can range from 20 degrees C. or lower up to 300 degrees C., butmore preferably less than 200 degrees C., while T₂ 136, 236 can rangefrom 200 degrees C. to 600 degrees C. or greater. The temperatureschosen depend on the reactants used and the types of films beingdeposited. Of course, T₁ 132, 232 could be the ambient temperature stateof the substrate initially and, as such, would not be initially heated.

The temperature ramp up rate 134, 234 during heating, α, is preferablyat least 200 degrees C./sec, and more preferably, higher. Thetemperature ramp down rate 138, 238 during cooling, β, is preferably atleast 100 degrees C./sec, and more preferably higher. In practice, α islarger than β.

The methods of the present invention can toggle the substrate surfacequickly between two or more temperatures to yield properly decoupledreactions. The energy may be delivered by ions, electrons, photons, orby a thermal energy means that primarily affects the top surface of thesubstrate undergoing deposition in a transient fashion. Sources forimparting such energy may come from rapid thermal processing (RTP) orlaser irradiation. An electron beam may similarly be used. Any of theseenergy-inducing methods serve to cause a rapid, transient heating of thesubstrate.

FIG. 3 shows an ALD system 300 schematic incorporating a lamp array 310for rapidly heating a substrate 360 and a chilled ESC 370 for rapidlycooling the substrate 360. A precursor A source 320, precursor B source330, and recirculating chiller 350 are shown. Means for valving andcontrolling 345 the pressure of the backside gas 340 are also shown.FIG. 3 shows a preferred method of heating the substrate in the mannerdescribed herein by rapid thermal processing. RTP refers to a process inwhich the heating cycle is very rapid and is typically performed vialamp array 310 utilizing graphite heaters, plasma arc, tungsten halogenlamps, or other means well known in the art. This RTP system 300 iscoupled to the substrate 360 such that the substrate 360 surface isbrought up to required temperature in seconds (as opposed to minutes fortypical isothermal processes) with typical temperature ramp rates of100-300 degrees C./sec.

FIG. 4 shows an ALD system 400 schematic incorporating amechanically-scanned laser 410 (coupled with substrate 360 rotation) forrapidly heating a substrate 360 and a chilled ESC 370 for rapidlycooling the substrate 360. Means for valving and controlling 345 thepressure of the backside gas 340 are also shown. FIG. 4 shows analternative embodiment where an infrared (IR), ultraviolet (UV), or deepultraviolet (DUV) laser 410 may be employed to rapidly heat a substrate360, whereby the beam is scanned rapidly over the entire area of thesubstrate 360. Alternatively, other forms of irradiation such asextreme-ultraviolet (EUV) or other radiation forms such as x-rays may beemployed.

The scanning means is accomplished by methods that are well known in theart. Alternatively, the substrate 360 can be moved with respect to thelaser 410 (such as rotating the substrate with respect to a laser linesource or point source) so that uniform irradiation of the substrate 360will occur or the laser 410 may simply scan the entire surface. Laser410 heating methods may locally heat a substrate 360 with temperatureramp rates of 200-700 degrees C./sec or greater—typically, higher thanRTP.

These rapid heating methods reduce the overall thermal budget of the ALDprocess since the substrate 360 is only at a peak temperature for ashort duration of time (on the order of seconds or less). This reducesthe overall thermal budget of the process and enables the use of peaktemperatures greater than if the substrate 360 was held at a constanttemperature for longer periods of time.

Regardless of the energy source used for heating the substrate 360, thesubstrate 360 must be rapidly cooled, preferably through the use of acooled pedestal. A cooled pedestal is a substrate 360 holder thatretains the wafer 360 or other substrate 360 against a cooled surfaceand introduces a “backside” gas 340, typically at pressures of 3-10torr, as a thermal heat transfer medium in the space 365 between them(i.e., the substrate and the cooled pedestal). Thermal coupling betweenthe substrate and pedestal generally increases for increasing gaspressure, but saturates at an upper limit, typically around 10-20 torrdepending on gas species, gap spacing, and geometry of the interface.Typical gases used are Ar and He. Although pedestals incorporating clamprings for retaining the wafer can be used, electrostatic chucks 370, arepreferred. ESCs 370 use electrostatic attraction to retain the waferwith a minimal substrate-pedestal gap distance and therefore attainbetter heat transfer than clamp ring systems. It is known that ESCs 370can be designed with cooling capacities of approximately 200-350 W/m² K.

In order to achieve the fast temperature ramp up rates discussedpreviously, the substrate 360 must at times be thermally decoupled fromthe cooled pedestal so that the energy input is not wasted in heating upthe large thermal mass of the pedestal. However, during fast temperatureramp downs, they must be coupled so that the cooled pedestal canefficiently remove heat from the substrate. Since the existence of abackside gas 340 is the primary means of heat transfer between thesubstrate 360 and the rest of the system in a vacuum or reducedatmosphere environment, a key part of this invention then is thisstate-based presence of the backside gas 340, or more specifically, thestate-based pressure control 345 of the backside gas 340. With suitablevalving and pressure control 345, application of substrate 360 backsidegas 340 will facilitate thermal coupling between the substrate 360 and acooled pedestal enabling the low temperature state. Valving off thebackside gas 340 thermally decouples the substrate 360 from the cooledpedestal so that a high temperature state can be quickly achieved duringlamp array 310 or laser 410 irradiation. This method is particularlyeffective in the semiconductor wafer processing industry since thethermal mass of the substrate 360 is very small, especially compared toa typical cooled pedestal, and the heat fluxes are so large. Thissequence is illustrated in FIG. 5.

FIG. 5 shows substrate temperature 520 in response to irradiation 500times 502 and 504 and state-dependent control of backside gas pressure510. FIG. 5 illustrates how the backside gas 340 in conjunction withirradiation 500 can be used to cause the substrate temperature 520 torapidly change from a low temperature to a high temperature and back toa low temperature state. The cooled pedestal can be cooled via chilledwater, gases, or refrigerants to a steady state temperature near orsignificantly below room temperature (e.g., −40 degrees C. to 20 degreesC.). The pedestal can also be simply maintained at a desired lowtemperature state greater than room temperature by, for example,resistively warming the heater. In either case, the heat transferringbackside gas 340 is used to toggle between the low temperature state 522(backside gas 340 is “high” 514, e.g., 3-10 torr) of the pedestal to thehigh temperature state 524 (backside gas 340 is “low” 512, e.g., muchless than 3 torr) during lamp array 310 or laser 410 irradiation.

It may be conceivable to perform the sequences described in FIGS. 1 and2 in separate RTP and ALD chambers. However, processing speed would becompromised. A preferable embodiment would be for the sequencesdescribed in FIGS. 1 and 2 to be carried out in a single chamber.

From the description of the preferred embodiments of the process andapparatus set forth herein, it will be apparent to one of ordinary skillin the art that variations and additions to the embodiments can be madewithout departing from the principles of the present invention.

1. A method for affecting a temperature of a substrate on a pedestal ina film deposition apparatus for rapidly cycling the temperature of saidsubstrate during an atomic layer deposition (ALD) process, thedeposition apparatus having a process chamber area for processing a topsurface of said substrate and having a substrate backside space betweensaid substrate and said pedestal, the method comprising: a. causing atemperature of said substrate to be at a first temperature bycontrolling irradiation of a top surface of said substrate with anenergy source and providing a heat transferring gas in said backsidespace between said pedestal and said substrate at a first pressure tocool said substrate, the heat transferring gas contacting a bottomsurface of said substrate, wherein said pedestal is maintained at asteady state temperature and cool relative to said substrate, whereinsaid heat transferring gas thermally couples said substrate to saidpedestal to remove heat from said substrate, wherein a gas pressure insaid backside space is different from a gas pressure in said processchamber area; b. introducing a first reactant gas into said processchamber area, such that substantially at least one monolayer of saidfirst reactant gas is adsorbed onto said substrate, wherein said firsttemperature is low enough to prevent decomposition of said firstreactant gas; c. evacuating any excess of said first reactant gas fromsaid process chamber area; d. causing a temperature of said substrate tobe at a second temperature by controlling irradiation of said topsurface of said substrate by said energy source and providing said heattransferring gas in said backside space between said pedestal and saidsubstrate at a lower pressure, relative to said first pressure, whilesaid pedestal remains maintained at the steady state temperature andcool relative to said substrate, wherein providing said heattransferring gas in said backside space between said pedestal and saidsubstrate at the lower pressure thermally decouples the substrate fromthe pedestal, wherein controlling the pressure of the heat transferringgas in said backside space in conjunction with controlling theirradiation of said top surface is the causation of the substratechanging between the first temperature and the second temperature,wherein a gas pressure in said backside space is different from a gaspressure in said process chamber area; e. introducing a second reactantgas into said process chamber area to react with said first reactant gasto deposit a monolayer of a single material over said substrate during asingle ALD cycle, wherein said second temperature is higher than saidfirst temperature, while the pedestal remains at the steady statetemperature, to cause a reaction between said first reactant and saidsecond reactant on the substrate to deposit a film of material on saidsubstrate; f. evacuating any excess of said second reactant gas fromsaid chamber; and g. repeating steps a through f to form successivefilms of said material on said substrate until said successive films areof a desired thickness.
 2. The method of claim 1, wherein said heattransferring gas is argon.
 3. The method of claim 1, wherein said heattransferring gas is helium.
 4. The method of claim 1, wherein said firstpressure is between about 3 and 10 torr.
 5. The method of claim 1,wherein said first pressure is between about 3 and 20 torr.
 6. Themethod of claim 1, wherein said lower pressure is less than 3 torr. 7.The method of claim 1, wherein said lower pressure is less than 1 torr.8. The method of claim 1, wherein said energy source is selected from agroup consisting of a rapid thermal processor, a laser, an electron beamsource, and an x-ray source.
 9. The method of claim 1, wherein saidsubstrate temperature is additionally affected by resistively heatingsaid pedestal.
 10. The method of claim 1, wherein said substratetemperature is additionally affected by flowing a chilled fluid throughsaid pedestal.
 11. The method of claim 1 wherein steps c and d areperformed concurrently.
 12. The method of claim 1 wherein, after steps athrough f are performed a first time in the film deposition apparatus,steps f and a are performed concurrently in subsequent cycles of steps athrough f.
 13. The method of claim 1 wherein steps d and e are performedconcurrently.